1. Field of the Invention
The invention relates to structures having super-phobic surfaces.
2. Related Art
Superhydrophobic surface structures are known for their ability to repel high surface tension liquids such as water. Some superhydrophobic surface structures have been made that include a plurality of raised structures that are spaced apart by interstices and held in positions relative to each other on a substrate. Raised structures may be formed having various shapes, including posts and ridges. When a liquid having a sufficiently high surface tension makes contact with a typical superhydrophobic surface structure, the liquid may form an interface with the superhydrophobic surface structure at a local contact angle sufficiently high so that the liquid does not immediately penetrate into the interstices. Liquids having a relatively high surface tension include water, ionic liquids, and glycerol, among others. On the other hand, when a liquid having a sufficiently low surface tension makes contact with a typical superhydrophobic surface structure, the liquid may form an interface with the superhydrophobic surface structure at a local contact angle sufficiently low so that the liquid immediately penetrates into the interstices. Liquids having a relatively low surface tension include gasoline, oils, alcohols such as methanol and isopropanol, alkanes, and other hydrocarbons, among others.
Much work has been done to develop potentially useful applications for superhydrophobic surface structures in order to exploit their non-wetting behavior when contacted by liquids having high surface tension. A liquid having a sufficiently low surface tension generally may wet a superhydrophobic surface structure, while a liquid having a sufficiently high surface tension may not do so. The ability of liquids having low surface tension to wet these surfaces constitutes a vulnerability often making the surfaces impractical for use outside a highly controlled laboratory environment. This vulnerability lies in the pervasiveness of liquids having low surface tension. As examples, human fingertips generally carry natural skin oils having low surface tension, in addition to any foreign materials present that may include low surface tension liquids such as hand lotion or oily food residues. Any contact of a fingertip with a typical superhydrophobic surface structure may contaminate the surface with low surface tension liquids, disabling the non-wetting behavior of the affected region of the superhydrophobic surface structure and also allowing high surface tension liquids such as water to then freely penetrate and wet the superhydrophobic surface structure. Atmospheric aerosols are another common and pervasive source of low surface tension liquids that can easily contaminate a superhydrophobic surface structure, especially in urban environments.
There is a continuing need for new types of super-phobic surface structures that can withstand contact by a liquid having a relatively low surface tension without immediately losing their liquid repelling ability.